Ammonia gas pressure booster

ABSTRACT

A system and method for delivering a reductant into an engine exhaust stream for use in the reduction of NO x  is disclosed. The system includes a cartridge having an interior space for storing the reductant containing material, a fluid supply line fluidly connected to the cartridge for receiving the reductant, a pressure boosting device for boosting the flow of reductant, a flow management device, and, an injector for injecting the reductant into an after-treatment system for combining with the exhaust stream. The reductant may include ammonia. Use of the pressure boosting device increases the reductant pressure into the aftertreatment system, providing for a reduction in the time to inject the reductant into the exhaust stream, while improving the distribution of reductant into the exhaust stream.

TECHNICAL FIELD

The present system and method relates to the delivery of a reducing agent or reductant into the exhaust stream of a vehicle for reduction of NO_(x) in the exhaust stream. Particularly, the system and method relates to the addition of a pressure boosting device within the reductant supply line to increase the pressure of reductant and improve reductant distribution within the exhaust stream.

BACKGROUND

Compression ignition engines provide advantages in fuel economy, but produce both NO and particulates during normal operation. New and existing regulations continually challenge manufacturers to achieve good fuel economy and reduce the particulates and NO_(x) emissions. Lean-burn engines achieve the fuel economy objective, but the high concentrations of oxygen in the exhaust of these engines yields significantly high concentrations of NO_(x) as well. Accordingly, the use of NO reducing exhaust treatment schemes is being employed in a growing number of systems.

One such system is the direct addition of a reductant or reducing agent, such as ammonia gas, to the exhaust stream. It is an advantage to deliver ammonia directly into the exhaust stream in the form of a gas, both for simplicity of the flow control system and for efficient mixing of the reducing agent, ammonia, with the exhaust gases. The direct use of ammonia also eliminates potential difficulties related to blocking of the dosing system, which may be caused by precipitation or impurities, e.g., in a liquid-based urea solution. In addition, an aqueous urea solution cannot be dosed at a low engine load since the temperature of the exhaust line would be too low for complete conversion of urea to ammonia (and CO₂).

A couple specific challenges with the direct injection of a gaseous reductant, such as ammonia, relate to dispersion and mixing of the reductant or reducing agent with the hot exhaust gases. Generally, the cartridge storing the reductant-containing material needs to be heated to a sufficient temperature level so that the released reductant has enough pressure to overcome the pressure of the exhaust stream upon injection. Thus, the dispersion issue considers how to deliver or spread ammonia to the greatest volume of flowing exhaust, while the mixing issue concerns how to create the most homogenous mixture of exhaust and ammonia to facilitate NO_(x) reduction.

Thus, the present system and method provide for a reduction in the time required to inject the reductant into the exhaust stream, as well as, improving the distribution of the reductant into the exhaust stream. Additionally, the present system and method result in a reduction in energy requirements for heating the cartridges and reductant-containing material to the necessary level. These and other problems are addressed and resolved by the disclosed system and method.

SUMMARY

There is disclosed herein a system and method which avoids the disadvantages of prior devices and methods while affording additional structural and operating advantages.

Generally, a system for delivering a reductant into an engine exhaust stream, is disclosed. The system comprises a canister having an interior space for storing the reductant containing material, a fluid supply line fluidly connected to the canister for receiving the reductant, a pressure boosting device for boosting the flow of reductant a flow management device, and, an injector for injecting the reductant into an after-treatment system for combining with the exhaust stream.

In an embodiment of the system, the pressure boosting device is a pump integrated within the fluid supply line.

In another embodiment of the system, the pump is integrated within the fluid supply line between the cartridge and the injector.

A method for reducing NO_(x) in an exhaust gas stream of a diesel-engine vehicle, is disclosed. The method comprises the steps of fluidly coupling components of an exhaust gas treatment system package to an engine exhaust gas system, wherein the components comprise a cartridge having an interior space for storing a reductant containing material, a conduit fluidly connected to the cartridge for receiving the reductant upon release from the material, a pressure boosting device for boosting the pressure of the reductant, a flow management device; and, an injector for injecting the reductant into the exhaust stream. The method further comprises the steps of increasing the flow of reductant through the pump and the flow management device, injecting gaseous ammonia into the engine exhaust gas system through the injector, and, reacting the reductant with the engine exhaust gas stream reducing the level of NO_(x) in the exhaust gas stream.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an exhaust gas NO_(x) reduction (EGNR) system;

FIG. 2 is a schematic of the ASDS portion of the EGNR incorporating the pressure boosting device of the present system.

DETAILED DESCRIPTION

Referring to FIG. 1, there is illustrated the general components of a reductant storage and dosing system, specifically an exhaust gas NO_(x) reduction (EGNR) system 10, which includes an ammonia storage and delivery system (ASDS) 50. The ASDS 50 involves delivery of gaseous ammonia to an after-treatment assembly 60, which is used in the reduction of NO_(x) in an engine exhaust gas stream as part of the EGNR system 10 found on combustion engine vehicles. The ASDS 50 is comprised of several components, including at least one ammonia-containing main canister or cartridge 20, which may be contained within a housing or storage compartment (not shown), an ammonia-containing start-up canister or cartridge 24 located on the outside of the housing, an ammonia flow module (AFM) 26, a peripheral interface module (PIM) 30, and possibly other components depending on vehicle specifications.

In addition to the ASDS 50, the EGNR 10 includes vehicle engine components, including an electronic control module 32. The specific components of the ASDS 50 and EGNR will not be discussed in further detail with the exception of discussing, as necessary, how a component or system may relate to the present system and method. Further, as the vehicle ignition system and the vehicle exhaust system, including those used on a diesel engine vehicle, are well-known, these systems also will not be described in detail.

In the ASDS system, the components for storing a reductant or reducing agent, including an ammonia adsorbing/desorbing material (not shown), stored within a main canister or cartridge 20. The present system may include a start-up canister 24, generally useful for the initial release of reductant into the exhaust stream before the main canister 20 or canisters reach the required temperature level to release its reductant. As heat is necessary to release the reductant or reducing agent from the adsorbing/desorbing material within the cartridge, it is useful to have a heating source, such as through an electrical source or an engine coolant sourced heater. Alternatively, the cartridge 20 may be placed within a heating unit or jacket or other type of housing for storage, heating and transport (not shown).

The ammonia adsorbing/desorbing material loaded into the main and start-up cartridges 20 and 24, respectively, is generally in a solid form, such as a compressed powder or granules, and may include any suitable shape for packing into the cartridges, including balls, granules, or a tightly-packed powder formed as a disk. Suitable adsorbing/desorbing material for use with the present system include metal-ammine salts, which offer a solid storage medium for ammonia, and represent a safe, practical and compact option for storage and transportation of ammonia. Ammonia may be released from the metal ammine salt by heating the salt to temperatures in the range from 10° C. to the melting point to the metal ammine salt complex, for example, to a temperature from 30° to 150° C. Generally speaking, metal ammine salts useful in the present device include the general formula M(NH₃)_(n)X_(z), where M is one or more metal ions capable of binding ammonia, such as Li, Mg, Ca, Sr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, etc., n is the coordination number usually 2-12, and X is one or more anions, depending on the valence of M, where representative examples of X are F, Cl, Br, I, SO₄, MoO₄, PO₄, etc. Preferably, ammonia saturated strontium chloride, Sr(NH₃)Cl₂, is used. While embodiments using ammonia as the preferred reductant are disclosed, the disclosure is not limited to such embodiments, and other reductants may be utilized instead of, or in addition to, ammonia for carrying out the system and method disclosed and claimed herein. Examples of such other, or additional reductants include, but are not limited to, urea, and ammonium carbamate.

As noted above, in order to use ammonia gas in the treatment of NO_(x) in an exhaust system, it is necessary to apply a sufficient amount of heat to the cartridges and the contained ammonia adsorbing/desorbing material, in order to release the ammonia into its useful gaseous form. Once released, the ammonia gas is delivered to the exhaust stream by way of a fluid tubing or conduit 34 connected at one end to the ammonia source (main or start-up canister) 20, 24 and at the other end to an injector 62 positioned within the after-treatment assembly 60 (FIGS. 1 and 2). Prior to reaching the injector, the reductant flows through a flow management device (ammonia flow modulator-AFM) 26. The AFM 26 generally comprises a housing 28 having an inlet 28 a, 28 b for each of the start-up unit 24 and main unit 20, respectively, and an outlet 28 c leading to the injector 62 and the after-treatment assembly 60. The AFM may also include a plurality of check valves, control valves and pressure release valves, as well as, a plurality of circuits and sensors, all of which are designed to facilitate the flow of a sufficient amount of ammonia gas to the exhaust after-treatment assembly 60.

In the present system, in order to increase the pressure and reduce the time for injecting the reductant into the exhaust stream, a pressure boosting device 100 is added to the system. Specifically, a pressure boosting device 100 is integrated to the fluid supply line 34. As shown in FIG. 2, the pressure boosting device 100 is a pump, which is integrated into the fluid supply line between the reductant source (main and start-up cartridges 20, 24) and the AFM 26. The addition of the pressure boosting device 100 results in an increase in the pressure of the reductant at the injector 62. Prior to use of the present pressure boosting device, the cartridges in the system needed to be heated to a level sufficient to create enough ammonia gas pressure to overcome the pressure of the exhaust stream. Addition of the pressure boosting device 100 increases pressure of the reductant for injection into the exhaust stream when the cartridge 20, 24 pressure is still below the pressure of the exhaust stream. Use of the pressure boosting device 100 allows for shorter periods of time before reductant can be injected and a reduction in energy required to heat the cartridge. The increase in reductant gas pressure at the injector 62 will also result in improved reductant distribution within the after-treatment system 60. Operation of the pressure boosting device 100 will be controlled by the electronic control module (ECM) 32 and powered by the vehicle's electrical system (not shown). Overall, use of the pressure boosting device results in shorter warm-up periods before reductant can be injected into exhaust streams, better distribution of reductant into the exhaust stream, and a reduction in the energy requirement to electrically heat the cartridge of the ASDS.

The present pressure boosting device 100 is useful in a method that reduces the amount of time need for the ASDS to be able to inject a reductant, such as ammonia, into the exhaust stream, while also improving the distribution of reductant in the exhaust stream. The present method includes the steps of fluidly coupling components of an exhaust gas NO_(x) reduction (EGNR) system package to an engine exhaust gas system, wherein the components comprise a cartridge 20 having an interior space for storing a reductant containing material, a conduit 34 fluidly connected to the cartridge for receiving the reductant upon release from the material, a pressure boosting device 100 for boosting the flow of reductant, a flow management device 26, and, an injector 62 for injecting the reductant into the exhaust stream flowing through an after-treatment assembly 60. The method further includes increasing the pressure of reductant through the pressure boosting device and the flow management device, injecting gaseous ammonia into the engine exhaust gas system through the injector, and, reacting the reductant with the engine exhaust gas stream thereby reducing the level of NO_(x) in the exhaust gas stream. In the present method, the pressure boosting device is a pump, which is integrated into the reductant supply line or conduit between the cartridge and the flow management device. 

What is claimed is:
 1. A system for delivering a reductant into an engine exhaust stream, the system comprising: a canister having an interior space for storing a reductant containing material; a fluid supply line fluidly connected to the canister for receiving the reductant; a pressure boosting device for boosting the flow of reductant; a flow management device; and, an injector for injecting the reductant into an after-treatment system for combining with the exhaust stream.
 2. The system of claim 1, wherein the reductant containing material is an adsorbing/desorbing material.
 3. The system of claim 1, wherein the reductant is ammonia.
 4. The system of claim 1, wherein the pressure boosting device is a pump integrated into the fluid supply line.
 5. The system of claim 4, wherein the pump is positioned between the canister and the flow management device.
 6. The system of claim 4, wherein the pump increases a pressure of the reductant at the injector.
 7. The system of claim 4, wherein the pump decreases injection time of the reductant into the exhaust stream.
 8. A method for reducing NO_(x) in an exhaust gas stream of a diesel-engine vehicle, the method comprising the steps of: fluidly coupling components of an exhaust gas NO_(x) reduction system package to an engine exhaust gas system, the components comprising: a cartridge having an interior space for storing a reductant containing material; a conduit fluidly connected to the cartridge for receiving the reductant upon release from the material; a pressure boosting device for boosting the pressure of the reductant; a flow management device; and, an injector for injecting the reductant into the exhaust stream increasing the flow of reductant through the pump and the flow management device; injecting gaseous ammonia into the engine exhaust gas system through the injector; and, reacting the reductant with the engine exhaust gas stream reducing the level of NO_(x) in the exhaust gas stream.
 9. The method of claim 8, wherein the pressure boosting device is a pump integrated within the conduit and positioned between the cartridge and the flow management device.
 10. The method of claim 9, wherein the pump increases the pressure of the reductant at the injector. 